We are studying the mitochondrial DNA from Crithidia fasciculata known as kinetoplast DNA. Using restriction enzyme mapping, DNA sequencing, and heteroduplex mapping, we are studying the organization of the minicircle sequences of this DNA. We are especially interested in determining the sequence of minicircle fragments which have extremely anomalous electrophoretic mobilities. These fragments may form unusual secondary structures. We are also studying the mechanism by which this DNA replicates. Our current view is that the minicircles do not replicate while attached to the network, but that they are dissociated from the network and then replicate as free minicircles. Subsequent to replication, they are reattached to the periphery of the network. We are studying the mechanism of replication of the individual free minicircles, and we are also attempting to isolate the enzymes responsible for removal of minicircles from the network and for reattachment of minicircles subsequent to replication.